Set field can still be used with container fields.
There are two different methods that can be used.
Set field can copy the container field contents from the current portal row (the row where you clicked a button to select the image) to the container field placed on the layout.
Set field can copy a primary key value from the portal's record to a match field in the layout's table and then the layout container field can be a field from the related table. This method requires two Tutorial: What are Table Occurrences? of the portal's table--one for the portal relationship and one to link to the container field placed directly on your layout.
I tried the second method and it worked. Thanks and God bless you.